Deeper insights into how the brain’s two hemispheres interact
Strokes are the second leading cause of death, and affect over 2 million people per year in Europe alone. Stroke diagnosis and clinical evaluations are performed with the help of neuroimaging, but predictions about recovery are limited. These predictions are particularly difficult when a patient suffers a stroke to one side of their brain. For many years, neuroscience has worked under the assumption that the functions of each hemisphere are markedly different: language is dominant in the left hemisphere, while visuospatial functions are more the domain of the right, for example. Yet advances in neuroimaging techniques and research – including with stroke data – have brought these assumptions under scrutiny. “The brain seems to possess a remarkable capacity for adaptation and compensation, with the precise mechanisms and factors governing these processes remaining subjects of ongoing research,” says Stephanie Forkel, researcher at France’s National Centre for Scientific Research (CNRS) and PERSONALISED project coordinator. In the PERSONALISED project, funded by the Marie Skłodowska-Curie Actions programme, researchers used neuroimaging and computational modelling to dive into the underlying links between the brain hemispheres. “Understanding these mechanisms holds great promise for improving stroke recovery and neurorehabilitation strategies,” adds Forkel.
Creating artificial lesions
PERSONALISED leveraged pre-existing high-resolution open-source neuroimaging and cognitive data from a robust data set of 1 200 healthy participants in the Human Connectome Project (HCP), the largest and most advanced data set in the field. The primary goals of PERSONALISED were to unveil the connection between brain anatomy and the dynamic variations in brain lateralisation, and to establish the association between this dynamism and the severity of symptoms and post-stroke recovery. First, the researchers measured functional and structural lateralisation in the healthy brain during unguided video viewing. They then simulated stroke impact through artificial lesions, and created a model evaluated against real-world neuroimaging and cognitive data from stroke patients. “These three research phases decoded the intricacies of individual-level brain lateralisation mechanisms, showcased the clinical advantages of advanced neuroimaging, and forged an exciting path for exploring dynamic brain mechanisms in future studies,” remarks Forkel.
Decoding the intricacies of brain connections
The research revealed that brain connections play a far more profound role than simply transmitting signals between brain regions. Rather, behaviour and cognition emerge from dynamic connections between cortical areas. “These interactions necessitate a delicate orchestration of local and distant brain regions through densely connected networks,” Forkel explains. “Consequently, brain connections serve as the foundation for the brain’s functional organisation.” In another groundbreaking outcome, the project illustrated how imaging connections within a living brain offer a unique window into the neurobiology of cognition, shedding light on brain evolution and the diversity of cognitive profiles between individuals and species.
Disconnectome
The research showed that brain pathologies can increase this variability through disconnections. “Consequently, the prediction of long-term symptoms now leans towards a focus on brain disconnections, marking a paradigm shift that challenges current brain models and redraws our brain maps,” notes Forkel. The team pioneered a novel method in cognitive neuroimaging called the ‘disconnectome’. This revealed key links in white matter connections for reading abilities, creating a highly predictive framework for reading deficits after brain damage. “These findings have the potential to reshape our understanding of the brain and contribute significantly to the field of neuroscience and clinical practice,” Forkel says.
Keywords
PERSONALISED, brain, hemispheres, stroke, recovery, data, disconnectome, lesions, connections
